Medical science has long sought effective treatments for disease conditions involving stenosis (narrowing or obstruction) of the lumen of an artery. This condition, known generally as an occlusion, occurs in patients suffering from atherosclerosis, which is characterized by an accumulation of fibrous, fatty or calcified tissue in the arteries, otherwise known as atheromata or plaques. An occlusion may be partial or total; it may be soft and pliable or hard and calcified. Occlusions can arise at a great variety of sites in the arterial system including the aorta, the coronary and carotid arteries, and peripheral arteries. An occlusion can result in hypertension, ischemia, angina, myocardial infarction, stroke and even death.
Minimally invasive procedures are the preferred treatment of arterial occlusions. In these procedures, a catheter—a long, highly flexible tubular device—is introduced into a major artery through a small arterial puncture made in the groin, upper arm or neck. The catheter is advanced and steered into the site of the stenosis. A great variety of devices have been developed for operating upon the stenosed artery, and these devices are placed at the distal end of the catheter and delivered thereby. Example procedures include percutaneous transluminal coronary angioplasty (PTCA), directional coronary atherectomy (DCA), and stenting.
In a total occlusion, a passageway must first be opened through the occlusion to allow the balloon/stent catheter to be placed in the target stenosed segment of the vessel. As occlusion morphology is complicated and varies from patient to patient, common methods and devices for opening these occlusions have limited success and require long procedures with potentially adverse effects on the patient. Such adverse effects include perforation of blood vessel wall, high radiation dose or damage to kidneys due to extensive use of angiographic contrast material.
Stenoses, or occlusions, are made of a variety of materials—from softer fatty substances such as cholesterol, to tougher fibrous material, to hard calcified material. Generally the ends of the occlusion—the proximal and distal caps—comprise the harder calcified material. The harder materials are more difficult to penetrate, requiring a significant amount of energy, the softer materials require less energy. Therefore, opening an occlusion requires transfer of relatively extensive energy to the distal end of a catheter or guide wire, especially when calcification is present. Additionally, the form of energy required to penetrate such an occlusion may differ from occlusion to occlusion, which differences generally are only realized during the procedure.
Some available methods for opening total occlusions are radio-frequency ablative energy (as used in system sold by Intralumenal Therapeutics as Safecross™), vibrational energy of about 20 kHz and small amplitudes (as used in system sold by FlowCardia Inc. as Crosser™), dedicated stiff guide wire which pushes a passage through the occlusion (as developed by Asahi Intec Co. and distributed as Confianza 9g/Conquest and Miracle 12g guide wires) and mechanical vibration elements working at high frequency (Crosser™). The latter suffer from significant energy loss between the energy source at the proximal end of the catheter and the driller located at the distal end of the catheter, as well as limited working life due to material fatigue. For example, with an ultrasound catheter, the ultrasonic energy usually originates from an ultrasound transducer at the proximal end of the catheter and is then transmitted to the distal head of the catheter as a sinusoidal wave, causing the distal head to vibrate and either ablate or disrupt the target occlusion. To reach treatment sites, such catheters must be rather long—about 150 cm or more—and therefore a large amount of energy must initially be transmitted to reach the distal end. At the same time, to be flexible enough to course through highly tortuous vessels, the wires must be reasonably thin. The long length and narrow diameter combine to make wire breakage a common problem due to the stress and wear from the high energy pulses. Guide wires stiff enough to penetrate hard occlusions have the disadvantage that their inflexibility and straight tips make navigating through tortuous vessels difficult and increase the risk of vessel perforation. All such devices provide limited success rate ranging from 40-70%.
Occlusions comprise a variety of materials of different density and hardness. Therefore, the nature of the energy used in a re-canalization device should suit the specific occlusion and the penetration should be controlled to prevent perforation of the artery walls or damage to healthy tissue. Additionally, because the energy originates at the proximal end of the catheter it must be able to reach the distal end of the device near the occlusion at a level sufficient to effect penetration of the occlusion without damaging the conductive wires and without sacrificing flexibility of the device. As previously described, current devices suffer either from an insufficient amount of energy transferred to the distal end of the device or a mismatch between the type of energy delivered and the type of occlusion, sometimes resulting in too much force being applied and thereby increasing the risk of damage, or even perforation, of the lumen wall. Accordingly, there is a need for a system or apparatus that can transfer adequate energy to the re-canalization device, and there is a need for a system that can adjust the amount of energy transmitted to the penetrating end of the device based on the hardness of the occlusion.
Additionally, because the total occlusion prevents blood flow to the vessel downstream of the occlusion, conventional X-ray fluoroscopy imaging is incapable of imaging both the occluded section of the vessel and the downstream portion of the vessel. Thus, there is also a need for an improved re-canalization system that is compatible with techniques permitting visualization of the re-canalization device and surrounding tissue during the PCI procedure.